1. Field of the Invention
This invention relates to chemical indicators, specifically indicators for the detection of vapor phase hydrogen peroxide.
2. Description of the Prior Art
U.S. Pat. No. 4,169,123 (Moore et al.) and U.S. Pat. No. 4,169,124 (Forstrom et al.) describe cold gaseous sterilization techniques using hydrogen peroxide gas as the sterilant. A primary concern to the operators of any sterilization equipment is whether or not the sterilizer functions properly to deliver the sterilant to the sterilization chamber. The need exists for an indicator which will detect the presence of hydrogen peroxide gas in the chamber and thus provide immediate verification that the sterilizer is operating correctly.
Test compositions and indicators for the detection of hydrogen peroxide in liquid solution are known in the art. U.S. Pat. No. 3,183,173 (Oakes) discloses a composition comprising an iodide salt, a metal catalyst and a high molecular weight polymer such as polyvinyl alcohol. Any hydrogen peroxide present in the test solution reacts with the iodide salt to produce free iodine. The iodine complexes with the polymer in the presence of the catalyst to produce a color change. U.S. Pat. No. 3,654,180 (Bauer) discloses an improvement on the indicator disclosed in the Oakes patent which uses .alpha.-naphthoflavone as the indicator dyestuff. Both the Oakes and Bauer indicator compositions rely on the complexing of free iodine with polymers in the presence of a metallic catalyst to produce a color change.
Soviet Union Patent No. 277,375 discloses an indicator strip which will detect the presence of hydrogen peroxide in the air. This strip is impregnated with a mixture of luminol, sodium carbonate and a copper catalyst. Luminol is a complex molecule which will emit light in the presence of hydrogen peroxide. A light producing reactant such as luminol does not undergo a permanent chemical transformation, reflected by a visible color change, upon exposure to hydrogen peroxide.
Color change as an indication that ozone sterilization is complete is known in the art. U.S. Pat. No. 3,704,096 (Verses et al.) teaches use of an aniline dye indicator strip and a cobaltous chloride indicator strip which are applied to an instrument to be sterilized in a transparent container. The strips react with ozone and humidity thereby undergoing color changes which verify that sufficient exposure occurred to effect sterilization. These indicator strips are unique to the detection of ozone and humidity and will not react with hydrogen peroxide.
Indicators which are used in ethylene oxide sterilization, another cold gaseous process, are incompatible with use in hydrogen peroxide vapor sterilization. Ethylene oxide indicators are based on a completely different chemical reaction than that which occurs during gaseous hydrogen peroxide sterilization. Thus, an indicator which detects ethylene oxide is not capable of detecting hydrogen peroxide vapor. Moreover, the concentration of hydrogen peroxide vapor sterilant is generally orders of magnitude lower than that of other gaseous sterilants. For example, the concentration of ethylene oxide required for sterilization is generally 600 mg/L compared to the maximum of 75 mg/L of hydrogen peroxide vapor disclosed in the Forstrom et al. patent referenced above. Thus, the indicators used in ethylene oxide sterilization would not respond to the low levels of hydrogen peroxide present during hydrogen peroxide gas sterilization, even if the chemical composition of the two sterilants were the same.
Similarly, the thermal indicators used in steam sterilization are based on a different chemical reaction than that of gaseous hydrogen peroxide sterilization and thus would not react with hydrogen peroxide. Steam sterilization is also a high temperature process (about 132.degree. C.); the thermal indicators utilized therein will not function in hydrogen peroxide gas sterilization which is a cold process usually conducted at temperatures below 80.degree. C.
It is an object of the present invention to provide an indicator for use in gaseous hydrogen peroxide sterilization systems. It is a further object of the present invention to provide such an indicator which will verify that vapor phase hydrogen peroxide sterilizers are operating properly by detecting the presence of hydrogen peroxide vapor in the sterilization chamber. It is a further object of this invention to provide an indicator which is simple to use and provides easily readable results.